1. Field of the Invention
The present invention relates to a link type variable stroke engine, and especially relates to a link type variable stroke engine in which a piston slidably fitted to a cylinder block; a crankshaft rotatably supported at a crankcase; and a rotary shaft having an axis parallel with the crankshaft, being rotatably supported at the crankcase, and being provided with an eccentric shaft at an eccentric position, are linked by a linking mechanism, the linking mechanism including: a sub connecting rod having a connection tubular part into which a crank pin of the crankshaft is relatively rotatably fitted, and being rotatably connected with the crank pin; a main connecting rod connecting the sub connecting rod and the piston; and a swing rod connecting the sub connecting rod and the eccentric shaft, and oil scattered in the crankcase is guided to a position between the connection tubular part of the sub connecting rod and the crank pin.
2. Description of the Related Art
In conventional reciprocating engines, an oil supply hole is formed at a big end of a connecting rod to lubricate a position between the big end of the connecting rod and a crank pin by using oil scattered in a crankcase. Since load caused by explosion in a combustion chamber is applied to the big end of the connecting rod, the oil supply hole is formed in a position at the big end of the connecting rod, the position deviated from the direction of application of the load.
On the other hand, a link type variable stroke engine has already been known through Japanese Patent Application Laid-open No. 2003-278567. In the link type variable stroke engine, a piston, a crankshaft and an eccentric shaft provided to a rotary shaft parallel with the crankshaft are linked by a linking mechanism including a sub connecting rod, a main connecting rod and a swing rod. The sub connecting rod includes a connection tubular part into which a crank pin is relatively rotatably fitted, and thus is rotatably coupled with the crank pin. The main connecting rod connects the piston and the sub connecting rod. The swing rod connects the sub connecting rod and the eccentric shaft. Such a link type variable stroke engine also requires an oil supply hole formed at the connection tubular part of the sub connecting rod to lubricate a position between the connection tubular part of the sub connecting rod and the crank pin by a splash lubrication system using oil scattered in a crankcase.
Meanwhile, in the link type variable stroke engine, reaction force from the swing rod is applied to the sub connecting rod in addition to load by in-tube pressure acting thereon from the main connecting rod. Accordingly, the resultant force of the load by such in-tube pressure and the reaction force is applied to an inner surface of the connection tubular part of the sub connecting rod. Here, the direction of application of the resultant force is determined by the angle between the main connecting rod and the sub connecting rod, the magnitude of the force applied from the main connecting rod to the sub connecting rod, the angle between the sub connecting rod and the swing rod, the magnitude of the force applied from the swing rod to the sub connecting rod, and is not fixed in an operation cycle of the engine. If the oil supply hole is provided in a wrong position, oil leaks out from the oil supply hole under application of the maximum load by the maximum in-tube pressure, bringing serious effects on lubrication.